This proposal outlines studies on the functinal and enzymatic consequences of interplay between components of the T cell receptor (i.e., TCR alpha and beta chains CD3gamma, delta, epsilon and the zeta chain) and their associated protein tyrosine kinases (PTKs) and other T cell surface molecules and their associated PTK or phosphatase activities. Our working hypothesis is that the TCR can send a variety of enzymatically and functionally distinct signals by recruiting different cell surface "co-receptor" or "accesory" molecules, along with their associated PTK activities, into a TCR based signaling complex. The expression and arrangement of counter receptors on the antigen presenting cell (APC) would dictate which co-receptors and associated PTK actiities would be recruited for TCR-mediated signaling and where they would be positioned within the complex. In this manner, functionally distinct TCR-mediated signals dictated by the APC could be generate. The following specific aims are designed to test this hypothesis by expressing normal and altered forms of proteins involved in co- receptor/accessory molecule assisted TCR-mediated signal transduction in the class II-restricted antigen specific BI-141 T cell hybridoma and the class II expressing FT5.7 L cell APC and measuring the effects on TCR- mediated signal transduction. Specificaly, we propose to: 1) express mutant forms of p56lck alone or along with CD4 in the class II-restricted BI-141 T cell hybridoma and analyze TCR-mediated tyrosine phosphorylation and IL-2 producton, 2) analyze TCR-mediated cell suicide and inhibition of spontaneous gowth in these transfectants, 3) analyze the functional consequences of engaging different co-receptor/accessory molecules along with the TCR in BI-141 and transfectants expressing modified p56lck by stimulating them with APC transfected with individual counter-receptors, 4) analyze CD3-epsilon- and zeta chain- associated kinase activities and their relative contributions to specific signaling when different co- receptor or accessory molecules are included in the TCR signaling apparatus. These studie should contribute to our basic understanding of how TCR-mediated signals result in distinct functional consequences. Such an understanding may result in the development of interventive immune therapies designed to enhance the immune response to tumors, to efficiently vaccinate against tumors, or to stimulate T cell malignancies to undergo cell suicide. Furthermore, elucidation of TCR activation may help us understand how tumors escape immune destruction or what normal regulatory processes fail when a T cell is transformed into a leukemia or lymphoma.